MSDN 示例：未编译的打开对话框

Question

尝试编译示例代码时出现错误：

为什么？

#include <windows.h>
#include <shobjidl.h> 

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow)
{
    HRESULT hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED |
        COINIT_DISABLE_OLE1DDE);
    if (SUCCEEDED(hr))
    {
        IFileOpenDialog *pFileOpen;

        // Create the FileOpenDialog object.
        hr = CoCreateInstance(CLSID_FileOpenDialog, NULL, CLSCTX_ALL,
            IID_IFileOpenDialog, reinterpret_cast<void**>(&pFileOpen));

        if (SUCCEEDED(hr))
        {
            // Show the Open dialog box.
            hr = pFileOpen->Show(NULL);

            // Get the file name from the dialog box.
            if (SUCCEEDED(hr))
            {
                IShellItem *pItem;
                hr = pFileOpen->GetResult(&pItem);
                if (SUCCEEDED(hr))
                {
                    PWSTR pszFilePath;
                    hr = pItem->GetDisplayName(SIGDN_FILESYSPATH, &pszFilePath);

                    // Display the file name to the user.
                    if (SUCCEEDED(hr))
                    {
                        MessageBox(NULL, pszFilePath, L"File Path", MB_OK);
                        CoTaskMemFree(pszFilePath);
                    }
                    pItem->Release();
                }
            }
            pFileOpen->Release();
        }
        CoUninitialize();
    }
    return 0;
}

Error C2664 'int MessageBoxA(HWND,LPCSTR,LPCSTR,UINT)': cannot convert argument 2 from 'PWSTR' to 'LPCSTR' MSDNTut_3-OpenFileDialogBox ...\msdntut_3-openfiledialogbox\msdntut_3-openfiledialogbox\source.cpp 34

Error (active) E0167 argument of type "const wchar_t *" is incompatible with parameter of type "LPCSTR" MSDNTut_3-OpenFileDialogBox ...\MSDNTut_3-OpenFileDialogBox\MSDNTut_3-OpenFileDialogBox\Source.cpp 34

Error (active) E0167 argument of type "PWSTR" is incompatible with parameter of type "LPCSTR" MSDNTut_3-OpenFileDialogBox ...\MSDNTut_3-OpenFileDialogBox\MSDNTut_3-OpenFileDialogBox\Source.cpp 34

微软 Visual Studio 社区 2017 版本 15.7.1 VisualStudio.15.Release/15.7.1+27703.2000 微软.NET框架版本 4.7.02556

已安装版本：社区

I fixed it by adding
#ifndef UNICODE
#define UNICODE
#endif
to the top.. I would still like an explanation on why that was necessary, please. ;)

另一个修复方法是将 "Character Set" 设置为 "Use Unicode Character Set"

项目->（项目名称）属性->常规->项目默认值->字符集

Answer 1

I fixed it by adding
#ifndef UNICODE
#define UNICODE
#endif
to the top.. I would still like an explanation on why that was necessary, please. ;)

MessageBox其实不是函数，是宏：

#ifdef UNICODE
#define MessageBox  MessageBoxW
#else
#define MessageBox  MessageBoxA
#endif // !UNICODE

因此，根据是否定义了 UNICODE，MessageBox() 映射到 MessageBoxW() (Unicode) 或 MessageBoxA() (ANSI)。您的项目未定义 UNICODE，因此使用了 MessageBoxA()，并且 PWSTR（指向宽字符串的指针）与 LPCSTR（指向窄字符串的指针）不兼容。

您可以改用 PSTR，或者像您一样启用 UNICODE 支持。

MSDN 示例：未编译的打开对话框

MSDN Example: The Open Dialog Box Not Compiling

c++

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